Sea creature confused for its lunch

Imagine being called a bag of chips, just because that was your last
supper. This unlikely fate befell an obscure marine worm, new research has
revealed1.

The amorphous greenish-yellow sea creature was wrongly classified as a
mollusc because specimens contained mollusc DNA and eggs. "Basically, the
mollusc material was lunch," explains animal evolutionist Maximilian Telford of
the University Museum of Zoology in Cambridge, UK.

Telford's team compared the DNA in fresh finds dredged up from soft mud
100 metres under a Swedish fjord. They conclude that the creature - called
Xenoturbella bocki - is a worm.

It is the most primitive existing member of the group to which humans
belong, called the deuterostomes, the authors argue. "It tells us what we
evolved from 500 million years ago," says Telford. Deuterostomes include
mammals, fish, starfish and worms.

The creature's rocky road to recognition began with its discovery more
than 80 years ago. It's lack of recognizable features - it has no separate
mouth or anus and no body cavity - led to its first labelling as a primitive
flatworm.

Subsequent studies related it to acorn worms and starfish, because of
similarities in its diffuse nerve network and outer epidermal layer. Then, in
1997, it received the lamentable mollusc moniker.

A preference for sludgy sea habitats makes Xenoturbella difficult to
find, so researchers can only guess at their numbers. "Quite possibly, they're
everywhere," says Telford, "but they're not the sort of thing you trip over on
a beach."